Owing to their soft feel and texture as well as high quality appearance, suede-like artificial leather products composed of ultrafine fibers and a polymeric elastomer have been used in a wide variety of applications including garments, furniture, and automobile interior materials. In recent years, there are increased demands for products of higher surface quality, particular for those having improved color unevenness owing to the use of ultrafine fibers and a polymeric elastomer of an identical color and maintaining high color fastness.
A generally used method for dyeing artificial leather is to dye artificial leather at a temperature at which ultrafine fibers are dyed most effectively in a dying machine, followed by washing or fixation treatment. This dying method, however, has the problem of inability to achieve effective coloring of polymeric elastomers, though being able to color ultrafine fibers effectively.
To solve this problem, there has been a proposal of an improvement in the conventional artificial leather method. Specifically, the dying method first dye artificial leather using a disperse dye in a dying machine and then perform treatment for reduction cleaning to produce artificial leather with high color developing ability, levelness of dyeing, and dyed color fastness (see Patent document 1).
In another proposal, artificial leather produced by forming a nap of polyester ultrafine fibers on one or both sides of an artificial leather base composed of a polyester fiber nonwoven fabric and an elastic polymer is first dyed with a disperse dye, then treated with a reduction agent to reduce and decompose the excess disperse dye, thereby decolorizing the elastic polymer parts exposed in the surface of the artificial leather base, subjected to oxidation cleaning with an oxidizing agent as required, and treated with hot water containing a surface active agent so that the dye contained in the elastic polymer in the artificial leather base moves to the surface of the elastic polymer (see Patent document 2).